Receiving circuit



June 11, 1929. 5 CQUTOULY 1,717.010

RECEIVING CIRCUIT Filed Dec, 30. 1922 //71/e/7f0r: GUS/0V6 C de Cou/ou/y Patented June 11, 1929.

UNITED STATES PATENT OFFICE.

GUSTAVE C. DE COUTOULY, OF GLEN RIDGE, NEW JERSEY, ASSIGNOR- TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF YORK, N. Y., A CORPORATION OF NEW YORK.

Application filed December 30, 1922.

The present invention relates to wave receiving systems. The invention more particularly relates to wave receiving systems of the general type employing frequency selectivity together with amplification of the received wave energy.

T heinvention finds particular application in high frequency receiving and amplifying systems, such as radio frequency amplifier systems and the like, although in its broadest aspects it is not limited to use in such systems.

In radio frequency amplifiers employing the well known electric discharge device amplifiers, a difficulty is presented by the tendency of the circuit to produce sustained oscillations, due to feeding back of some of the amplified energy to the input side of the circuit. The feeding back of the energy may take place by any kind of coupling relation between the output and input sides of the amplifiers, but a common form of coupling, and one that is particularly diflicult'to compensate for, is that due to the internal capacity of the amplifying devices. If the tendency to develop sustained oscillations is very marked, it is impossible to realize a high degree of amplification of the received radio frequency energy, since the amplifiers must be operated to give a smaller amplification than that at which the sustained oscillations occur. The production of these sustained os cillations is commonly known as singing.

A principal object of the invention is to decrease the tendency to sing in a circuit such as an amplifier circuit of the type referred to.

It has been found that singing in a high frequency amplifier circuit is in large part due to the fact that the energy fed back through an amplifier, for example, is applied to the tuned receiving circuit on the input side of the amplifier in such phase relation as to augment the wave in this tuned circuit due to the received energy.

A feature'of the invention resides in the association of the tuned receiving circuit with the remainder of the circuit in such manner that any energy fed back into the tuned circuit is inelfectual in producing singing or sustained oscillations.

Reference will now be made to the accompanying drawing for a. more detailed de- RECEIVING CIRCUIT.

Serial No. 609,893.

Fig. 1 shows a radio receiver including an open antenna, and

Fig. 2 illustrates a loop antenna which may be connected to the terminals 2 and 3 of F 1.

The drawing shows a radio frcquencv re ceivmg set, the general arrangement of which is well known. Any suitable type of wave receptor may be used. A. grounded antenna 1 is specifically illustrated.

The antenna 1 includes an inductance 4 to which the inductance 5 may be coupled. The coupling between the elements 4.- and 5 is preferably variable and the various elements in the circuit of antenna 1, such as the condenser 6 and inductance 4, may each be va riable in a manner well known in the art. The inductance 5, which for convenience may be termed the coupling inductance, is included in a resonant circuit comprising, in ad dition to the coupling inductance, the variable condenser 7 and a second inductance 8, which will be termed a loading inductance, connected in series to constitute a closed loop circuit tuned to the frequency of the wave to be received.

The loading inductance S is illustrated as eing placed at right angles to the coupling inductance 5, and it is preferable to relate these inductances in this manner in order that they may be out of mutual inductive relation to each other.

By including a loading inductance in the resonant circuit, the number of turns of wire in the coupling inductance 5 for the same tuning of the resonant circuit is smaller and the coupling adjustment between the coils 4 and 5 is more sensitive on account of the small self-inductance of the coil 5. The con nection between the inductance 8 and the terminal 2, as well as the winding 5, is by means of a switch 9 which connects to the point 10.

Connected with. the loop tuned circuit 5, 7, 8 is the amplifying and receiving circuit proper, con'iprising, in the form illustrated, two stages of high frequency amplification 11 and 12, a detector 13. and an audio-frequency amplifier M to which the indicating receiver 15 is connected, this being shown in the form of the well known head set.

The discharge devices 11, 12, 13 and 14 may be similar to each other in construction and are shown as of the well known thermionic discharge tube type. These tubes have their value of this potential is equal to the drop of 13 is preferably connected across a portion of the battery 18.

The grids of the various discharge devices are shown connected to different points in the filament heating circuit, and by virtue of such connections and of the filaments being connected in a series relation, the normal potential about which each grid operates with respect to its filament may be fixed at a desired value. The detector tube 13 is shown provided with a grid leak circuit 19 for aiding the detecting action of this tube.

The filament circuit of the tubes has a connection. by way of conductor 20 to ground and also to the tuned circuit 5, 7, 8, at the junction point 21 between the condenser 7 and the loading inductance 8. The grid of the first radio frequency amplifier 11 is connected to the terminal 10 of the resonant circuit 5, 7, 8.

The operation of the circuit in receiving and amplifying high frequency energy without singing will now be described.

Assuming first that the antenna 1 is used as the wave collector, the received high frequency wave is transferred by means of the coupling between 4 and 5 into the resonant selectin circuit 5, 7, 8, this circuit being tuned to the frequency of the wave which it is desired to receive. A high frequency potential -is set up betwen the points 10 and 21 by this high frequency wave and this difference of potential is impressedacross the filament and grid of the first high frequency amplifier 11.

It will beobserved that the instantaneous potential through the loading inductance 8, or what is the same thing, the drop of potential at the same instant across the coupling inductance 5 and the tuning condenser 7 in series.

The wave applied to the discharge device 11 is amplified'in accordance with the well understood action of the thermionic device 11, and is impressed on the grid of the tube 12 through the medium of the high frequency transformer 22. After further amplification inthe high frequency amplifier 12 the wave is transmitted through the radio frequency transformer 23 into the grid circuit of the detector 13. Thedetectedaudio-frequency component is transmitted through the audio-frequency transformer 2 1 into the grid circuit of the amplifier 14-, and the amplified audio-frequency signal is heard in the telephone 15.

The condenser 27, associated with the detector 13, and the condensers 28 and 29, in shunt of the battery 18, serve as radio frequency by-passes.

The transformers 22 and 23 are preferably constructed and designed, with respect to their own shunt 'capacity and inductance values and to the capacity of the tubes 11 and 12, to possess a resonant characteristic at the frequency of the wave. being amplified. These transformers may therefore serve to exert a further selecting action on the received Wave.

It has been found advantageous to make these radio frequency transformers by taking two wires and winding them together on a suitable spool of, say, one inch diameter as two parallel strands in close proximity, the wires being suitably insulated from each other as by enamel, silk, or cotton coverings. The finished winding then has four terminals, of which the two at the extremities of one winning are taken as primary and the other two as secondary terminals. Coils wound in this manner have sufficient capacity between primary and secondary windings, a; well as sufficient shunt capacity, to cooperate with the capacity of the tubes to constitute a radio frequency filter having a resonance band characteristic over a considerable range of wave lengths. This band effect may be increased by making the transformers between successive stages with slightly displaced resonance peaks. If a transformation ratio different from unity is desired, one of the windings may be continued for the necessary number of turns after the other is stopped.

In ractice, with the particular type of tube used, it has been found advantageous to make the first stage radio frequency transformer with a primary of 110 turns of No. 36 B and S gauge insulated wire and a secondary of 150 turns of the same; and to make the second stage transformer with a primary of 180 turns and a secondary of 240 turns of the same size wire. These figures, however, are not to be taken as in any wise limiting the invention.

The energy flowing in the windings of the transformers 22 and 23 is of greater amplitude than that in the tuned selecting circuit 5, 7, 8. Due to the inherent capacity between the elements of each of the devices'11 and 12, there is a high frequency path between the output side of each of these tubes to the input side of tube 11. Considering tube 11, for example, the capacity between the anode and grid of this tube provides a path to ground or to the cathode circuit which includes the circuit 5, 7, 8. In general it has been customary heretofore to connect the grid and filament of the tube 11 across the condenser 7 of the loop resonant select ing circuit. lVhen this is done the energy fed back through the high frequency path above traced is applied across the condenser T and in phase with the high frequency wave in the'tuned selecting circuit received from the antenna circuit.

lVith the type of connection of the present the high frequency path above traced to the tuned selecting circuit is applied between the points 10 and 21, and it will be noted that this voltage applied across only a portion of the total inductance of the resonantcircuits 5, 7, 8 instead of across the entire inductance according to prior practice. Not only is this true, but as pointed out above, the portion 5 of the inductance out of mutual inductive relation with the portion 8.

IVhatever theory of operation be adopted to account for the action, the invention has been found in practice to reduce singing in high frequency amplifiers in a very effective manner. In a particular circuit that the applicant has used, the coil 5 was made up of twenty turns of No. 24. B and S gauge wire and the coil 8 of forty turns of No. 24 wire, each of these coils being on cylindrical tubing of two and one half inches diameter. The primary coil comprised seventy turns of No. 24. wire on a tubing of three inches diameter, and the tuning condenser had a capacity of 0 to 800 micro-micro-farads. This set was operated for wave lengths of 250 to 550 meters. It will be understood that these figures are given only by way of example, and that they in no way limit the invention.

If a loop antenna as shown in Fig. 2 is used as the wave collector, its terminals will be connected to the terminals 2 and 3, as described above, and the switch 9 will be opened to disconnect the loading inductance S from the circuit. The loop ordinarily consists of a simple inductance which may be considered as replacing the loading inductance 8 in the resonant circuit 5, 7, 8. Keeping in mind that the antenna 1 is disassociated from the circuit and that the loop inductance takes the place of the loading inductance 8, theresonant circuit comprising 5, 7 and the loop antenna operates in precisely the same manner as the circuit 5, 7, 8 of Fig. 1.

IVhat is claimed is:

1. In combination an energy receptor, a resonant circuit comprising a path including a cmidenser and coupling inductance in series and a loading inductance in shunt to said path, but out of mutual inductive relation with. said coupling inductance, said coupling inductance being associated with said receptor in energy transfer relation, and a receiving circuit connected in shunt of said loading inductance.

2. In a wave amplifying system employing a vacuum tube having an anode, a cathode and a grid or impedance controlling element, a resonant circuit for supplying a voltage wave to said grid and cathode, said resonant circuit being tuned. to the frequency of the received waves and comprising at least two inductances out of mutual inductive relation with each other and a capacity, and a circuit associated with said anode and cathode and possessing resonance characteristics at the frequency at which said first mentioned resonant circuit resonates, said grid and cathode being connected in energy transfer relation across one of said inductances for reducing the tendency of the system to sing.

'3. In a radio frequency receiving system, a wave collecting circuit, a tuned circuit comprising a capacity, a coupling inductance, and a loading inductance separate therefrom and out of mutual inductive relation with said coupling inductance, said coupling inductance being associated with said wave collecting circuit in energy transfer relation, a radio frequency amplifier having a cathode, an anode, and a grid or control element, said grid and cathode being connected to elect-rically remote points on said loading inductance.

4. In a radio receiving system, a Wave collecting and selecting system including a resonant circuit having a condenser and at least two inductances out of mutual inductive relation with each other, a wave repeating device associated with said resonant circuit, an indicating receiver supplied with energy from said device, a resonant circuitbetween said device and said receiver, and means for reducing the tendency of said system to produce self-sustained oscillations, comprising means for connecting said device in shunt of one of said inductances.

5. In a radio receiving system, a wave collecting and selecting system including a condenser and an inductance and another inductance out of mutual inductive relation with the first inductance, said elements being in series and together being resonant at the frequency of the wave to be received, an indicating receiver, a Wave repeating device between said collecting system and said receiver and possessing inherent capacity, and means for transferring energy from said Wave collecting system to said wave repeating device, and for reducing the transfer of waves in the reverse direction, comprising means for connecting said repeating device in shunt of said series inductance and condenser.

6. In a wave amplifying system employing a vacuum tube having a cathode, an anode, and a control element, a resonant circuit including an inductance to which the Waves to be amplified are applied, a condenser and a second inductance out of mutual inductive relation with said first mentioned inductance, and a radio frequency transformer associated with said anode and cathode of said vacuum tube and possessing a resonance characteristic at the frequency at which said resonance circuit resonates, said control element and said cathode being connected in energy transfer relation across said second inductance for reducing the tendency of the system to sing.

7. In an amplifying system, a closed circuit and means to impress a wave thereon comprising an inductive winding included in said circuit, a second inductive Winding included in said circuit and possessing higher inductance than the first and out of mutual inductive relation with said first mentioned induc- 5 tive Winding, capacity means also included in said circuit of such value as to resonate with said inductive windings at the frequency of the wave to be amplified and an amplifying device having its terminals connected across said second inductive Winding. 10

In Witness whereof, I hereunto subscribe my name this, 28th day of December, A. D.

GUSTAVE (11in COUTOULY. 

